Alright, before diving in, let's get a solid plan for your database design. You need to decide if each tenant gets their own database or if they share one but with separate schemas. For instance, if your app handles sensitive info, you might want to go with separate databases for better isolation.

Head over to the Supabase dashboard and start a new project. You'll need to give it a name and set a password. Plus, you can pick where your server will be located. Easy peasy.

In your new project, go to the "Database" section. This is where you'll set up your tables and their relationships. If you're going with shared databases but separate schemas, create a new schema for each tenant.

Next, hop over to the "Auth" section. Here, you'll define how users log in and what roles they have. Make sure each tenant gets a unique role that only lets them access their own data.

Supabase does the heavy lifting by auto-generating a RESTful API for your database. Check out the "API" section to see your endpoints. Don't forget to set up access controls in your app logic so tenants can only see their own stuff.

Now, install the Supabase Client Library in your app. This library gives you methods to interact with the Supabase API. Use it for CRUD operations on your database and to handle user authentication.

Finally, give your multi-tenant setup a good test. Try scenarios like one tenant attempting to access another's data and make sure all your access controls are working as they should.

Always stick to best practices for security and data isolation in multi-tenant apps.